The present invention relates generally to a control system for a refrigeration apparatus and in particular to an improved control circuit for automatically controlling the operation of an ice making machine in a refrigeration apparatus.
Ice making machines for refrigeration apparatus typically operate in the following manner. When a control in the storage bin calls for more ice cubes, the condensing unit is activated which turns on the compressor to cool the ice cube cups or forms. The pump and agitator motor (if one is used) are also activated to spray water into the cups while the spray is agitated back and forth over the cups to promote the production of clear ice. This step in the process is referred to as the "freeze" cycle.
When the cups become filled with ice, the machine goes into a defrost cycle or what is commonly referred to as the "harvest" cycle. During this cycle, hot water and/or hot gas from the condensing unit are directed around the ice cups, which causes the ice cubes to fall out of the cups into the storage bin. The process continues until the control in the storage bin indicates that the storage bin is full. A more detailed description of the operation of an ice making machine of the type generally described herein is contained in U.S. Pat. No. 3,791,163, issued Feb. 12, 1974, and assigned to the assignee of the present invention.
It is the primary object of the present invention to provide an improved control circuit for an ice making machine of the above described type which is capable of accurately and reliably controlling the size of the ice cubes produced, thereby optimizing the cycle times, reducing the number of cycles required to fill the bin and thus reducing the overall operating time of the machine. In particular, the control circuit according to the present invention is fully automatic and utilizes a timing circuit to control both the freeze and harvest cycles. Moreover, the timing circuit is in turn controlled by the temperatures of the ambient air and the inlet water so that the time periods of the freeze and harvest cycles are varied accordingly. In this manner, the uniformity in the size of the ice cubes produced can be accurately controlled without the need for the more expensive and complicated cube size control apparatus.
Generally, the present control circuit includes two sequentially connected timers, one for controlling the freeze cycle and the other for controlling the harvest cycle. Each timer has a variable time period which is varied in accordance with the resistance values of one or more temperature responsive resistance devices adapted to respond to the temperatures of the ambient air and the inlet water. Thus, when either the temperature of the ambient air or the inlet water changes, the cycle times of the freeze and harvest cycles are adjusted accordingly. In addition, the preferred embodiment of the present invention utilizes an additional temperature responsive resistance device to control the activation of the condenser fan during the harvest cycle so that the refrigerant gas directed around the ice cups is maintained at a high temperature to promote the defrosting or release of the ice cubes from the cups.